Production of bright metallic deposits



Patented Oct. 8, 1946 PRODUCTION OF BRIGHT METALLIC DEPOSITS Meyer L. Freed, Ansonia,

New Haven,

and Oscar A. Stocker, Conn., assignors to The Seymour Manufacturing 00., Seymour, Conn.

No Drawing. Application April 15, 1940, Serial No. 329,724

27 Claims. l

This invention covers the applicability of thiourea and its derivatives as brightening agents for inclusion in electroplating baths of nickel, to the method of electroplating from such baths and the articles resulting therefrom, and also includes simultaneous use of such agents with sulfonated aryl aldehydes or with sulfonated aryl compound brightening agents free of the aldehyde group and particularly to the combined use of a thiourea substance, a sulfonated aryl aldehyde and a sulfonated aryl compound brightening agent free of the aldehyde group.

While the invention is generally applicable to the electrodeposition of nickel, its immediate important applicability is in the electrodeposition of nickel. Therefore, for convenience the invention may be illustrated by its use in nickel plating, although it is not to be restricted thereto.

Many attempts have been made to obtain the direct electrodeposition of a so-called bright nickel on a base metal from plating baths in which individual specifically suggested agents for the purpose have been tried. While progress in the desired direction is being made in a limited degree,

there is still some desired characteristic in the finished product, which has not yet been attained, for example, much has been desired with respect to covering power in the methods heretofore employed.

According to the instant invention it has been found that the addition of a thiourea to an aqueous acid solution comprising essentially a nickel material selected from the sulfate or chloride, or mixture of the sulfate or chloride of the metal brings about a resulting direct outstanding bright electrodeposit therefrom, possessing unusually satisfactory hiding power in covering up well the surface imperfections, depressions, scratches or blemishes found in the base metal prior to the electroplating.

While thiourea itself is admirably suitable for the indicated purpose, other compounds derived from it may also be used. Such compounds may be generically referred to as thiourea substances or broadly as to individual examples as a thiourea substance. Among those applicable are substituted thioureas such as those in which one or more of the hydrogen atoms of either or both amino groups is replaced, for example, by a hydrocarbon residue, which may be saturated or unsaturated. alkyl or aryl, such as that resulting from the removal of an hydroxyl radical from a saturated or unsaturated aliphatic alcohol or from an aromatic hydroxy compound. Thus diethylthiourea illustrates the staturated alkyl substituted thiourea, allylthiourea represents the unsaturated alkyl substituted thiourea, and phenylthiourea represents the aryl substituted substance.

Thiourea or other suitable thiourea substance may be used as the sole brightening agent in the plating bath of the nickel group metal. For example, it may be used in the regular Watt's .bath containing per gallon 37 ounces single nickel salts (sulfate), 8 ounces nickel chloride and 5 ounces of boric acid, within the limits of current density of about 5 to about amperes per square foot, temperature from about to F. and pHrange from about 3 to about 5 (electrometric) in amounts from about 0.3 gram thiourea per liter of the plating bath to about 1.5 grams per liter with possible variation somewhat below and somewhat above. The resulting electro deposit has good brightness to brilliance and excellent covering-and hiding power. Under some circumstances, it may be found that there is a tendency for the deposit to be pitted. This tendency is decreased by using a suitable wetting agent to reduce the surface tension of the plating bath to increase the opportunity for the hydrogen gas to leave the surface of themetal. Under some other circumstances when thiourea, or other thiourea substance, is used alone, the deposit has a tendency toward undesirable brittleness so that it is advisable that strain on the plated metal be avoided.

The thiourea substance may be used together with another agent such as a sulfonated aryl compound brightening agent which does not contain an aldehyde group such as a monoor polysulfonated monoor polynuclear aromatic compound containing either the benzene or naphthalene nucleus, such as benzene sulfonates as benzene sulfonic acid, benzene disulfonic acid, toluidine sulfonic acids, tolidine sulfonic acids, naphthalene sulfonic acids, naphthol sulfonic acids, or naphthylamine sulfonic acids, or mildly chlorinated derivatives of such sulfonic acids, of which examples include also alpha and beta napthalene monosulfonic acids, the 1,5 and 2,7 naphthalene disulfonic acids, alpha naphthylamine trisulfonic acid, Z-amino toluene 5-sulfonic acid, 2-amino toluene 4-su1fonic acid, 4-amino toluene 2-sulfonic acid, o-tolidin disulfonic acid, and napthalene 1,5 disodium sulfonate, all of which may be employed as the free sulfonic acid or as a salt thereof such as that obtained by replacing the hydrogen of the sulfonic acid radical by its equivalent of a salt forming cation such as a metal, for example, an alkali metal as sodium or potassium, or an alkaline earth metal as magnesium. or a nickel group metal as nickel, cobalt or iron, or an amine type cation including ammonium and those derived from amine or alkylamine as methylor ethylamine, or from an aikylolamine as mono-, di-, or triethanolamine, or other suitable salt forming base, all of which sulfonic acid compounds may be broadly referred to as a sulfonated aryl brightening agent free of the aldehyde group.

A Watts bath containing nickel sulfate and chloride and boric acid in amounts indicated above and per liter from about 0.3 gram to about 1.5 gms. of thiourea substance such as thiourea together with from about 1 gram to about grams of sulfonated aryl brightening agent free of the aldehyde such as naphthalene 1,5 disodium sulfonate, operated under the ranges of temperature, pH and current density included above yields a bright deposit with good hiding and covering power. These solutions with solely these two specific brightening agents can be controlled somewhat more evenly and uniformly than those with the thiourea substance alone and bring about somewhat less brittleness in the deposit. Thus, while they do have good covering power, they are not free of brittleness under all circumstances.

It is also possible to use the thiourea substance along with solely one other agent such as a sulfonated aryl aldehyde such as a monoor polysulfonated monoor poly-nuclear aryl aldehyde, of which the polynuclear type is exemplified by the sulfonated naphthaldehydes or anthraldehydes, and of which specially desired are the mononuclear derivatives, among which sulfonated cinnamaldehyde illustrates the unsaturated alkyl or vinyl type, and others are exemplified by sulfonated salicyialdehyde and other sulfonated benzaldehydes, including the saturated alkylated compounds, such as tolualdehyde, or especially the non-alkylated compounds as ortho-sulfobenzaldehyde, or the alkoxylated derivative as in sulfonated para-methoxy benzaldehyde (anisaldehyde). The nickel salt of 2,5-disulfobenzaldehyde illustrates the polysulfonated form, These sulfonated aryl aldehydes may be employed either as the free sulfonic acid derivative or as a salt thereof such as that obtained by replacing the hydrogen of the sulfonic acid radical by its equivalent of a salt forming cation of the scope hereinabove disclosed.

The thiourea substance can be used together with a sulfonated aryl aldehyde in the ordinary Watts bath with thiourea employed between about 0.02 gram and about 1.5 grams per liter and, for example, ortho-sulfobenzaldehyde at from about 1 gram to about 30 grams per liter, and preferably at least 2 grams per liter over a wide pH range including preferably from about 2.5 to about 4.5, although not restricted thereto. The tendency toward pitting is still observed although practically completely avoided with the preferred ranges just noted and there i some improvement in ductility over the plate obtainable by the use of thiourea and naphthalene 1,5 disodium sulfonate.

However, the most satisfactory results in the use of a thiourea substance are obtained when such substance is employed together with both the sulfonated aryl aldehyde and the sulfonated aryl brightening agent free of the aldehyde so that the plating bath contains at the same time all three of these difierent types of brightening agents. By using the combination of all three types pitting is avoided, 81.1 a very ductile, un-

Example 1 Nickel sulfate (6H2O) per gal-lon 37 Nickel chloride (6H20) do 8 Boric acid do 5 Naphthalene 1,5-disodium sulfonate grams per liter 2 Ortho-sulfobenzaldehyde do 3 Thiourea do 0.05

Current density 30-50 amperes per square foot; temperature 120 F.; pH 3.5-4.0 (electrometric).

Ezvample 2 The thiourea of Example 1 was replaced by 0.08 gram per liter of allylthiourea.

Example 3 The thiourea of Example 1 was replaced by 0.08 gram per liter of ethylthiourea.

Example 4 The thiourea of Example 1 was replaced by 0.1 gram per liter of phenylthiourea.

The amount of the nickel sulfate in any of the illustrative plating baths may vary from about 28 to about 50 ounces per gallon, the nickel chloride from about 3 to about 8 ounces per gallon, and the boric acid from about 2 to about 5 ounces per gallon. While the respective ranges of current density, temperature and hydrogen ion concentration given in Example 1 are preferred, the current density may vary from about 5 to about '75 amperes per square foot, the temperature from about 110 to about F., and the pH from about 3.0 to about 4.5 (electrometric) Instead of the combination nickel sulfate and chloride bath of Example 1, it is possible to use an equivalent nickel sulfate bath without any nickel chloride, or an equivalent nickel chloride bath without any nickel sulfate. In the baths of Examples 1 through 4 and in the straight nickel sulfate or straight nickel chloride baths, the naphthalene 1,5-disodium sulfonate may be varied between about 2 to 20 grams per liter or may be replaced by any other specific agent of the particular type. So also the ortho-sulfobenzaldehyde may vary from about 3 to about 10 grams per liter or may be replaced by any other specific aldehyde of the particular type, and the thiourea substance may be varied between 0.02 to about 0.10 gram per liter. The thiourea substance content may also vary between about one one-hundredth percent and about one and one-half percent of the nickel salt content of the bath.

When each individual agent is used alone it has certain advantages and certain drawbacks. The sulfonated aryl aldehyde brings about unusual throwing power, yet it has limited covering power yielding at times a so-called transparent plate. At the same time it exhibits a depolarizing action, acting as an anti-pit to prevent pitting. There may be reason to believe that it reacts with the hydrogen at the cathode exercising an oxidizing action. The sulfonated aryl brightening agent free of the aldehyde when used by itself gives a good brightness and good ductility and appears to be a carrier or maintenance agent by virtue of which the solution is more evenly and uniformly operated for it does not appear to plate out. The thiourea substance, used by itself brings about extreme brilliance, unusual covering power, but leaves a rather brittle plate.

The combination of the three above individual types at one time in the same bath gives an extremely bright, surprisingly ductile, very adherent plate with exceptionally good hiding power. It is unexpected that so small an amount of the thiourea substance in the combination of the three agents permits the unusual ductility and the exceptional hiding power. The influence of the presence of the sulfonated aryl aldehyde avoids the necessity of employing a wetting out agent, although one may be used if it is desired to lower the surface tension. With the resultant hiding power the use of a promoter metal such as cadmium or zinc may be entirely avoided.

The unusual hiding power obtained by the use of the combination permits an elegant deposit directly on steel, even on a poor grade of steel, without pre-plating with copper, or polishing or buffing. It makes it possible to plate all poorly finished surfaces and directly on unpolished steel, unbuifed copper, zinc die-castings, bright-dipped surfaces as well as matte finishes, also on brass, copper, copper-plated zinc die-castings and on dull nickel plated zinc die-castings. In decorative plating where thickness of nickel is not of extreme importance, a real brilliant deposit can per liter, each of said cooperating agents being present in a quantity relative to the other sufiicient to permit such deposit to be obtained under the operating conditions.

.3. An aqueous, acid electroplating bath .which comprises in the aqueous medium a nickel ion yielding material selected from the group of nickel sulfate, nickel chloride, and a mixture of nickel sulfate and nickel chloride, said bath having the capability of permitting a brilliant cathodic deposit of nickel to be obtained upon the passage be built up in the shortest time. The addition of the thiourea substance has permitted saving in time, current and anode consumption. No agitation of the bath is necessary and a minimum of supervision and of a simple order is required because the sulfonated aryl aldehyde still exerts its effective depolarizing activity, thus avoiding the cost of a wetting agent, and the sulfonated aryl brightening agent free of the aldehyde still exerts its beneficial efiect causing ease and control of the operation of the bath. The combination exhibits unusual throwing power enabling the deposit to reach and adequately and uniformly to cover the most intricate surfaces and the innermost exposed surfaces of the oddest shaped articles.

While the invention has been illustrated by description of specific embodiments of it, it is understood that many modifications, alterations, combinations and equivalents may be employed within the scope of the invention, covered by the appending claims.

We claim:

1. An aqueous electroplating bath for producing by electrodeposition under acid conditions a brilliant, cathodic deposit of nickel, which bath comprises in addition to nickel ion yielding material selected from nickel sulfate, nickel chloride, and a mixture of nickel sulfate and nickel chloride, a thiourea as the brightening agent and in a concentration less than about one and one-half grams per liter but in a quantity suflicient to permit a brilliant deposit of nickel of unusually satisfactory hiding power to be obtained under the operating conditions.

2. An aqueous, acid electroplating bath which comprises in theaqueous medium a nickel ion yielding material selected from the group of nickel sulfate, nickel chloride, and a mixture of of an electric current through the bath under the operating conditions, said capability being imparted thereto by the inclusion therein of cooperating addition agents, one of which is a thiourea present in a concentration from about 0.3 to about 1.5 grams per liter, and the other being a sulfonated aryl compound brightening agent free of the aldehyde group in a concentration from about 1 to about 10 grams per liter, each of said cooperating agents being present in a quantity relative, to the other suficient to permit such deposit to be obtained under the operating conditions, said deposit having somewhat less tendency toward brittleness than that of the deposit obtained when a thiourea is used alone as the brightening agent.

4. The method of electrodepositing a brilliant, cathodic deposit of nickel having unusually satisfactory hiding power, which method comprises passing an electric current from the anode to the cathode through an aqueous, acidv plating bath comprising in the aqueous medium essentially nickel ion yielding material selected from nickel sulfate, nickel chloride, and a mixture of nickel sulfate and nickel chloride, in the presence of a thiourea as the brightening agent in a concentration less than about one and one-half grams per liter but in a quantity sufficient to permit such brilliant deposit of nickel to be obtained under the operating conditions.

5. The method of electrodepositing a brilliant, practically pit-free, cathodic deposit of nickel, which method comprises passing an electric current from the anode to the cathode through an aqueous, acid plating bath comprising in the aqueous medium essentially nickel ion yielding material selected from nickel sulfate, nickel chloride, and a mixture of nickel sulfate and nickel chloride, in the presence of cooperating addition agents, one of which is a thiourea present in a concentration from about 0.02 to about 1.5 grams .per liter, and the other being a sulfonated aryl aldehyde in a concentration from about 1 to about 30 grams perliter, each of said cooperating agents being present in a quantity relative to the other sufficient to permit such deposit to be obtained under the operating conditions.

6. The method of electrodepositing a brilliant, practically pit-free, cathodic deposit of nickel as in claim 5, in which the thiourea in the bath is thiourea and the sulfonated aryl aldehyde is ortho-sulfobenzaldehyde.

'7. The method of electrodepositing a brilliant,

7 cathodic deposit or nickel, which method comprisespassing an electric current from the anode to the cathode through an aqueous, acid plating bath comprising in the aqueous medium essentially nickel ion yielding material selected from nickel sulfate, nickel chloride, and a mixture of nickel sulfate and nickel chloride, in the presence of cooperating addition agents, one of which Le a thiourea, present in a concentration from about 0.3 to about 1.5 grams per liter, and the other being a sulfonated aryl compound brightening agent free of the aldehyde group in a concentration from about 1 to about grams per liter, each of said cooperating agents being present in a quantity relative to th other sufilcient to permit such deposit to be obtained under the operating conditions, said deposit having somewhat less tendency toward brittleness than when a thiourea is the sole brightening agent.

8. The method of electrodepositing a brilliant, cathodic deposit of nickel as in claim 7, in which the thiourea in the bath is thiourea and the other cooperating agent is a naphthalene disodium sulionate.

9. An aqueous, acid electroplating bath which comprises in the aqueous medium a nickel ion yielding material selected from the group of nickel sulfate, nickel chloride, and a mixture of nickel sulfate and nickel chloride, said bath having the capability of permitting a brilliant, ductile, practically pit-free, cathodic deposit of nickel to be obtained upon the passage of an electric current through the bath under the operating conditions, said capability being imparted thereto by the inclusion therein of cooperating addition agents, one of which is a thiourea present in a concentration from about 0.02 to about 0.1 gram per liter, a second of which is a sulfonated aryl aldehyde in a concentration of about 3 to about 10 grams per liter, and the third is a sulfonated aryl compound brightening agent free of the aldehyde group in a concentration from about 2 to about grams per liter, each of said cooperating agents being present in a, quantity relative to that of the others to permit such deposit to be obtained under the operating conditions.

10. LAD. electroplating bath as in claim 1, in which the thiourea is selected from thiourea and thiourea in which at least one of its hydrogen atoms is replaced by a hydrocarbon residue.

11. An electroplating bath as in claim 1, in which the thiourea is selected from thiourea and thiourea in which at least one of its hydrogen atoms is replaced by a hydrocarbon residue selected from saturated and unsaturated aliphatic and aromatic residues.

which the sulfonated aryl aldehyde is a sulfonated phenyl aldehyde.

15. An electroplating bath as in claim 2, in which the thiourea, is thiourea and the sulfonated aryl adheyde is orthosulfobenzaldehyde.

16. An aqueous electroplating bath as in claim 3, in which the sulfonated aryl compound bright- 8 ening agent free of the aldehyde group is a naphthalene sulionic acid.

17. An aqueous electroplating bath as in claim 3, in which the sulfonated aryl compound brightening agent free of the aldehyde group is a naphthalene disulfonic acid.

18. An electroplating bath as in claim 3, in which the thiourea is thiourea and the other agent is naphthalene-1,5-disulfonic acid disodium salt.

19. An aqueous, acid electroplating bath which comprises in the aqueous medium a nickel ion yielding material selected from the group consisting of nickel sulfate, nickel chloride, and a mixture of nickel sulfate and nickel chloride, together with thiourea in a concentration from about 0.02 to about 1.5 grams per liter, said thiourea having the capability 0f permitting a brilliant cathodic deposit of the metal to be obtained upon the passage or an electric current through the bath, under the operating conditions.

20. The method of electrodepositing as in claim 4, in which the thiourea is selected from thiourea and substituted thioureas.

21. The method of electrodepositing as in claim 4, in which the thiourea is selected from thiourea and derivatives of thiourea, in which at least one of its hydrogen atoms is replaced y a hydrocarbon residue.

22. The method of electrodepositing as in claim 4, in which the thiourea is thiourea present in a concentration from about 0.02 to about 1.5 grams per liter.

23. An electroplating bath as in claim 9, in which the sulfonated aryl aldehyde is a sulfonated phenyl aldehyde and the sulfonated aryl compound free of the aldehyde group is a naphthalene sulfonic acid.

24. An electroplating bath as in claim 9, in which the sulfonated aryl aldehyde is a sulfonated benzaldehyde and the sulfonated aryl compound free of the aldehyde group is a naphthalene disulfonic acid, and the thiourea is thiourea.

25. An electroplating bath as in claim.9, in which the thiourea is thiourea, and the sulfonated aryl aldehyde is ortho-sulfobenzaldehyde and the third agent is naphthalene-l-Ei-disulionic acid sodium salt.

26. A nickel electroplating bath addition agent composition comprising a thiourea and a sulfonated benzaldehyde, said addition agent composition being capable, upon addition to an aqueous, acid nickel plating bath containing nickelion yielding material selected from the group of nickel sulfate, nickel chloride, and a mixture or nickel sulfate and nickel chloride, of causing a brilliant, practically pit-free cathodic deposit of nickel to be obtained upon the passing of an electric current from the anode through said bath to the cathode when the total concentration of the thiourea in said bath is less than one and onehalf grams per liter and of the sulfonated benzaldehyde is between about 1.0 and about 30.0 grams per liter.

27. A nickel electroplating bath brightening addition agent as claimed in claim 26, wherein the thiourea ingredient is thiourea itself and the sulfonated benzaldehyde ingredient is orthosulfobenzaldehyde.

MEYER L. FREED. OSCAR A. STOCKER. 

